RandomX/doc/isa-ops.md

RandomX instruction listing

Integer instructions

For integer instructions, the destination is always an integer register (register group R). Source operand (if applicable) can be either an integer register or memory value. If dst and src refer to the same register, most instructions use imm32 as the source operand instead of the register. This is indicated in the 'src == dst' column.

Memory operands are loaded as 8-byte values from the address indicated by src. This indirect addressing is marked with square brackets: [src].

frequency	instruction	dst	src	src == dst ?	operation
12/256	IADD_R	R	R	src = imm32	dst = dst + src
7/256	IADD_M	R	mem	src = imm32	dst = dst + [src]
16/256	IADD_RC	R	R	src = dst	dst = dst + src + imm32
12/256	ISUB_R	R	R	src = imm32	dst = dst - src
7/256	ISUB_M	R	mem	src = imm32	dst = dst - [src]
9/256	IMUL_9C	R	-	-	dst = 9 * dst + imm32
16/256	IMUL_R	R	R	src = imm32	dst = dst * src
4/256	IMUL_M	R	mem	src = imm32	dst = dst * [src]
4/256	IMULH_R	R	R	src = dst	dst = (dst * src) >> 64
1/256	IMULH_M	R	mem	src = imm32	dst = (dst * [src]) >> 64
4/256	ISMULH_R	R	R	src = dst	dst = (dst * src) >> 64 (signed)
1/256	ISMULH_M	R	mem	src = imm32	dst = (dst * [src]) >> 64 (signed)
8/256	IMUL_RCP	R	-	-	dst = 2x / imm32 * dst
2/256	INEG_R	R	-	-	dst = -dst
16/256	IXOR_R	R	R	src = imm32	dst = dst ^ src
4/256	IXOR_M	R	mem	src = imm32	dst = dst ^ [src]
10/256	IROR_R	R	R	src = imm32	dst = dst >>> src
4/256	ISWAP_R	R	R	src = dst	temp = src; src = dst; dst = temp

IMULH and ISMULH

These instructions output the high 64 bits of the whole 128-bit multiplication result. The result differs for signed and unsigned multiplication (IMULH is unsigned, ISMULH is signed). The variants with a register source operand do not use imm32 (they perform a squaring operation if dst equals src).

IMUL_RCP

This instruction multiplies the destination register by a reciprocal of imm32. The reciprocal is calculated as rcp = 2x / imm32 by choosing the largest integer x such that rcp < 264. If imm32 equals 0, this instruction is a no-op.

ISWAP_R

This instruction swaps the values of two registers. If source and destination refer to the same register, the result is a no-op.

Floating point instructions

For floating point instructions, the destination can be a group F or group E register. Source operand is either a group A register or a memory value.

Memory operands are loaded as 8-byte values from the address indicated by src. The 8 byte value is interpreted as two 32-bit signed integers and implicitly converted to floating point format. The lower and upper memory operands are marked as [src][0] and [src][1].

Memory operands for group E registers are loaded as described above, then their sign bit is cleared and their exponent value is set to 0x30F (corresponds to 2^-240).

frequency	instruction	dst	src	operation
8/256	FSWAP_R	F+E	-	(dst0, dst1) = (dst1, dst0)
20/256	FADD_R	F	A	(dst0, dst1) = (dst0 + src0, dst1 + src1)
5/256	FADD_M	F	mem	(dst0, dst1) = (dst0 + [src][0], dst1 + [src][1])
20/256	FSUB_R	F	A	(dst0, dst1) = (dst0 - src0, dst1 - src1)
5/256	FSUB_M	F	mem	(dst0, dst1) = (dst0 - [src][0], dst1 - [src][1])
6/256	FSCAL_R	F	-	(dst0, dst1) = (-2x0 * dst0, -2x1 * dst1)
20/256	FMUL_R	E	A	(dst0, dst1) = (dst0 * src0, dst1 * src1)
4/256	FDIV_M	E	mem	(dst0, dst1) = (dst0 / [src][0], dst1 / [src][1])
6/256	FSQRT_R	E	-	(dst0, dst1) = (√dst0, √dst1)

FSCAL_R

This instruction negates the number and multiplies it by 2x. x is calculated by taking the 5 least significant digits of the biased exponent and interpreting them as a binary number using the digit set {+1, -1} as opposed to the traditional {0, 1}. The possible values of x are all odd numbers from -31 to +31.

The mathematical operation described above is equivalent to a bitwise XOR of the binary representation with the value of 0x81F0000000000000.

Denormal and NaN values

Due to restrictions on the values of the floating point registers, no operation results in NaN or a denormal number.

Rounding

All floating point instructions give correctly rounded results. The rounding mode depends on the value of the fprc register:

fprc	rounding mode
0	roundTiesToEven
1	roundTowardNegative
2	roundTowardPositive
3	roundTowardZero

The rounding modes are defined by the IEEE 754 standard.

Other instructions

There are 4 special instructions that have more than one source operand or the destination operand is a memory value.

frequency	instruction	dst	src	operation
7/256	COND_R	R	R	if(condition(src, imm32)) dst = dst + 1
1/256	COND_M	R	mem	if(condition([src], imm32)) dst = dst + 1
1/256	CFROUND	fprc	R	fprc = src >>> imm32
16/256	ISTORE	mem	R	[dst] = src

COND

These instructions conditionally increment the destination register. The condition function depends on the mod.cond flag and takes the lower 32 bits of the source operand and the value imm32.

mod.cond	signed	condition	probability	x86	ARM
0	no	src <= imm32	0% - 100%	JBE	BLS
1	no	src > imm32	0% - 100%	JA	BHI
2	yes	src - imm32 < 0	50%	JS	BMI
3	yes	src - imm32 >= 0	50%	JNS	BPL
4	yes	src - imm32 overflows	0% - 50%	JO	BVS
5	yes	src - imm32 doesn't overflow	50% - 100%	JNO	BVC
6	yes	src < imm32	0% - 100%	JL	BLT
7	yes	src >= imm32	0% - 100%	JGE	BGE

The 'signed' column specifies if the operands are interpreted as signed or unsigned 32-bit numbers. Column 'probability' lists the expected probability the condition is true (range means that the actual value for a specific instruction depends on imm32). Columns 'x86' and 'ARM' list the corresponding hardware instructions (following a CMP instruction).

CFROUND

This instruction sets the value of the fprc register to the 2 least significant bits of the source register rotated right by imm32. This changes the rounding mode of all subsequent floating point instructions.

ISTORE

The ISTORE instruction stores the value of the source integer register to the memory at the address specified by the destination register. The src and dst register can be the same.